Expecting the land's carbon absorption to make up for emissions from burning fossil fuels masks the need for real climate action, say scientists in Australia.

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Just as people pump greenhouse gases into the atmosphere by burning fossil fuels, the land also absorbs some of those emissions. Plants, as they grow, use carbon dioxide and store it within their bodies.

However, as the Climate Council’s latest report shows, Australia’s fossil fuels (including those burned overseas) are pumping 6.5 times as much carbon into the atmosphere as the land can absorb. This means that, while storing carbon on land is useful for combating climate change, it is no replacement for reducing fossil fuel emissions.

Land carbon is the biggest source of emission reductions in Australia’s climate policy centrepiece – the Emissions Reduction Fund (ERF). This is smoke and mirrors: a distraction from the real challenge of cutting fossil fuel emissions.

Land carbon

Land carbon is part of the active carbon cycle at the Earth’s surface. Carbon is continually exchanging between the land, ocean and atmosphere, primarily as carbon dioxide.

In contrast, carbon in fossil fuels has been locked away from the active carbon cycle for millions of years.

Carbon stored on land is vulnerable to being returned to the atmosphere. Natural disturbances such as bushfires, droughts, insect attacks and heatwaves, many of which are being made worse by climate change, can trigger the release of significant amounts of land carbon back to the atmosphere.

Changes in land management, as we’ve seen in Queensland, for example, with the relaxation of land-clearing laws by the previous state government, can also affect the capability of land systems to store carbon.

Burning fossil fuels and releasing CO₂ to the atmosphere thus introduces new and additional carbon into the land-atmosphere-ocean cycle. It does not simply redistribute existing carbon in the cycle.

The ocean and the land absorb some of this extra carbon. In fact, just over half of this additional carbon is removed from the atmosphere, and split roughly equally between the land and the ocean. However, this leaves almost half of the CO₂ emitted from fossil fuel combustion in the atmosphere. It’s this remaining CO₂ that is driving global warming.

Figure 2. Changes in the global carbon cycle from 1850 to 2014. Positive changes (above the horizontal zero line) show carbon added to the atmosphere and negative changes (below the line) show how this carbon is then distributed among the ocean, land and atmosphere. Adapted from Le Quere et al. 2015, data from CDIAC/NOAA-ESRL/GCP/Joos et al. 2013/Khatiwala et al. 2013.

Although Australia’s land sector has absorbed more carbon than it has emitted over the past decade or two, this has been overshadowed by our domestic fossil fuel emissions and those from our exported fossil fuels. These are roughly 6.5 times greater than the uptake of carbon by Australian landscapes.

Under international carbon accounting protocols, emissions are assigned to the country that burns the fossil fuels. However, many Australians are becoming increasingly concerned about the ethics associated with exploiting our fossil fuels, no matter where they are burned.

In short, we’ve got a big problem that requires a global response, which includes a strong commitment from Australia.

Falling short of our commitment

Last December, Australia joined the rest of the world in pledging to do everything possible to limit global warming to no more than 2°C above pre-industrial levels, and furthermore to pursue efforts to limit the increase to 1.5°C.

Current climate change policies and practices in Australia allow for the use of land carbon “offsets” – that is, carbon taken up by land systems can be used to offset or subtract from fossil fuel emissions.

For example, the government’s ERF provides financial incentives for organisations or individuals to adopt new practices or technologies that reduce or sequester greenhouse gas emissions.

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Australia’s fossil fuels are pumping 6.5 times as much carbon into the atmosphere as the land can absorb…while storing carbon on land is useful for combating climate change, it is no replacement for reducing fossil fuel emissions.

If this rate is continued, total fossil fuel emissions from 2015 to 2050 will be about 360 billion tonnes – nearly 10 times larger than the maximum estimated biological carbon sequestration of 38 billion tonnes over the same period.

It is now virtually certain that the carbon budget (the amount of carbon that can be produced while keeping warming below a certain level) will be exceeded. To meet the Paris 1.5°C aspirational target (and probably to meet the 2°C target) will require the use of negative emission technologies throughout the second half of the century.

However, no proposed negative emission technology has yet been proven to be feasible technologically at large scale and at reasonable cost, so this approach remains an in-principle option only. For effective climate action, the emphasis must remain on reducing emissions from fossil fuel combustion.

Using land carbon to “offset” our fossil fuel emissions is ultimately a smokescreen for real climate action.

Our thanks to Jacqui Fenwick for co-authoring this article and the report.